Diamond D-JET Winglets - Technical Close-up
Style and Function
Few D-JET topics have generated as many customer questions over the past several months as the presence or absence of winglets on the flight test aircraft. The D-JET Proof-of-Concept (serial number 001) sported an initial winglet design that also was used on serial number 002 in its early days. Early photos of S/N 002 showed the aircraft with winglets. In late fall 2007, Diamond removed the winglets to test the aircraft with more “standard” wingtips while the winglets were being redesigned. As photos of the winglet-less S/N 002 and, later, S/N 003 aircraft became available,
many customers – some with considerable passion – asked whether the D-JET would permanently fl y sans winglets.
Winglets are now back, as the cover headline proclaims. They’re based on a refined design and are now undergoing fl ight test. With the expectation that the D-JET as certifi ed will, indeed, sport winglets, this technical close-up article – authored by Diamond Aircraft’s head of Flight Sciences – provides some good context for this stylish yet very functional D-JET structural feature.
Winglet Background and History
Winglets are wingtip-mounted drag reduction devices commonly found on many modern business jets, general aviation aircraft, and commercial airliners. When a wing generates lift, it also generates drag, called “lift-induced drag”. On a humid day, you can actually see one artifact of this drag – white vortices rolling off the tips of the wings and fl aps. The more lift a wing generates, the stronger these tip vortices are (or, for the technically inclined, the greater the shed vorticity). Winglets reduce the strength of these tip vortices so they reduce the induced drag of an aircraft.
Depending on the aircraft speed, weight and altitude, a signifi cant percentage of the overall aircraft drag can be due to lift-induced drag. Given the D-JET’s flight envelope, most of this induced drag occurs during climb and long-range cruise. Reducing lift-induced drag also can contribute to improved fuel economy, longer range, and potentially shorter landing and takeoff distances – all of which contribute to the D-JET’s overall affordability and utility.
The winglets on D-JET S/N 002 are a second-generation design. An initial set of winglets were designed for the Proof of Concept aircraft. Lessons learned in terms of performance and manufacturability have been incorporated into the new design. For example, the tip-mounted anti-collision and strobe lights are now mounted internally for reduced drag. The shape and angle also have been refined.